The present invention relates to a portable sign stand with a pivoting sign support mechanism that increases the stability of the stand when the stand is subjected to loads such as wind pressure or vehicular contact.
Highway safety signs are often displayed on portable sign stands in the vicinity of temporary highway conditions, such as construction activity or road damage, to notify drivers of the upcoming danger. Portable highway safety sign stands are generally designed to be lightweight, sturdy and collapsible so that they may be quickly set up or taken down, readily moved, and easily stored when not in use. The stands generally include a base supported on collapsible legs, and a sign support member extending upward from the base for displaying a sign. When used on a road with fastmoving traffic, the stands may be subjected to heavy wind loads produced by passing traffic, and may also be run over by passing vehicles or construction equipment. A number of mechanisms have been developed to prevent the signs from being toppled or damaged by such forces and to protect from injury the drivers of vehicles that run over the stands. Generally, the mechanisms function by providing a location at which the sign stand may flex or pivot in response to the application of a force, in combination with some means for returning the sign to a vertical position after the force is removed. The most common mechanisms involve the use of a flexible member or pivotal joint disposed at some point between the base and a sign supported on the sign support member, coupled with a spring for returning the sign support member to its vertical position.
Portable sign stands for displaying highway safety signs are generally designed with safety, stability and durability as primary goals. First, the sign stands should be designed to be as safe as possible for both users and occupants of passing vehicles. For instance, the springs used to tension the sign support member in a vertical position are often very stiff. The flexing of these springs may open up pinch points that may injure an unwary user when the spring returns to its neutral position. Thus, the spring should be designed to protect users from this type of injury. More importantly, if a vehicle strikes a stand, the stand may cause injury to the occupants of the vehicle or damage to the vehicle. For instance, if the vehicle hits the stand with enough speed, the stand may come over the hood of the vehicle and strike the windshield. Thus, these stands should be designed to withstand an impact from a vehicle, yet minimize the potential of injury to the occupants of the vehicle.
Stability is another important concern for portable highway safety sign stands, as the stands should resist being blown over by wind from passing vehicles. When a sign stand is subjected to a wind load, moments are created about the points where each leg of the stand meets the ground. In a heavy wind, these moments may be large enough to topple a sign over its legs. One way to reduce these moments is to lengthen the legs of a stand. However, this reduces the portability and storability of the stand. Thus, another method of increasing the stability of a sign stand would be desirable.
Finally, the portable stands should be designed to be as durable as possible. The pivoting mechanisms of the sign stands must be strong enough to withstand the constant pivoting caused by heavy traffic conditions. The springs used in these mechanisms are particularly susceptible to stress and strain. Over time, these springs may fail and require replacement, which may be expensive.
The life of a spring in a stand is related to the type of stresses to which the spring is subjected. For instance, many stands utilize bending mechanisms, in which a spring is tensioned by bending when the sign support member pivots, to return the sign to a vertical position. One type of bending mechanism incorporates a vertical leaf spring into the sign support member. The leaf spring may bend when a sign on the stand is subjected to a load, dispersing the force from the load. However, this type of stand has the disadvantage that the spring may be damaged if a vehicle runs over the stand, as the leaf spring may not be able to bend sufficiently for a sign mounted to the stand to fit beneath the vehicle without damaging the spring.
Another type of bending mechanism uses a coil spring attached in an upright position to a base, with a sign support member mounted to the top of the spring. An example of this type of sign stand is disclosed in U.S. Pat. No. 4,038,769 to Werner. When this type of stand is bent, one side of the coil spring is compressed and the other side is stretched. It may be possible to bend these springs far enough to position a sign mounted to the stand parallel to the road surface, but such a severe deflection may damage the spring. Moreover, the unequal stresses caused by this type of spring motion may lead to the premature fatigue or failure of the spring.
In both of the configurations described above, the spring serves the dual function of supporting the sign and resisting deflection. A third type of sign stand uses a coil compression spring mounted between the sign stand base and the sign supporting member in such a way that the spring does not directly support the sign, but only functions to resist deflection. An example of this type of sign stand is described in U.S. Pat. No. 4,676,015 to Stoudt. Stoudt discloses a sign stand that utilizes an off-center pivot mechanism with a compression spring disposed midway up the sign support post. This stand has the advantage that the spring is compressed rather than bent, which may extend the life of the spring. However, the pivoting mechanism of this stand is positioned high on the sign support member, so that the sign stand may cause damage to a vehicle, or may itself be damaged, if struck. Furthermore, the stand is designed such that the pivot points would still be relatively high off of the base even if the pivoting mechanism were mounted to the base. Also, the off-center pivot mechanism of Stoudt has exposed pinch points where the top of the sign support member rests on the pivot mechanism that may injure an unwary user.
Thus, there remains a need for a durable and highly stable portable sign stand that provides safety features for the protection of both users and occupants of passing vehicles.